Equipping an item will undo dispel of constant effect invisibility
Equip an item with a constant effect invisibility enchantment, dispel the invisibility effect (e.g. by talking to an NPC), then equip (or unequip) any item that is not the one that gave you invisibility. The invisibility effect returns.
(RM-3456 from redmine: created on 2016-06-29 by scrawl ., , closed on 2016-06-29 by Miroslav Remák)